Raw sausages are defined in the guidelines of the German Food Codex as “reddened sausage products which are storable without refrigeration, and generally eaten raw. With a ripening of raw meat, combined with drying out, they have become sliceable or spreadable”. A distinction is made between sliceable raw sausage (e.g. Salami, Plockwurst, Cervelatwurst or Landjäger) and spreadable raw sausage (e.g. Teewurst or Mettwurst).
In the case of ripening, a distinction is made between slow ripening, standard ripening and rapid ripening. In rapid ripening, for the reddening, conventionally glucono-δ-lactone is admixed which reduces the pH in the emulsion in the course of a few hours (to about pH 5.6). The acidification can also be accelerated by adding sugar to the emulsion.
Customarily, a conventionally ripened raw sausage requires about 14 to 20 days for ripening, depending on its diameter and the type of ripening, until it is ready for sale. Slow ripening is 4 to 8 weeks and more.
Ripening is completed when the water content has fallen below a certain level. It is known that meat and sausage emulsion give off water most rapidly in the time period up to reaching the isoelectric point, i.e. in a time period in which the pH falls from about 5.8 to about 5.3. At the pH 5.3 (isoelectric point of the meat), the meat proteins form a gel which impairs the further release of water. The time period up to reaching the isoelectric point, or the point of maximum coagulation of the meat proteins, is therefore optimum for drying the sausage.
In order to achieve the most rapid possible decrease in water content, casings having a water permeability of 600 to about 1600 g per m2 and a day are used. These are generally cellulose fiber skins or collagen skins. These casings are also used for the production of mold-ripened raw sausage, in particular mold-ripened salami.
In the first 24 hours the pH scarcely falls during the standard ripening (that is without addition of acidulants) and remains constant at about 5.8. By means of a suitable temperature profile, the fall in pH can be further retarded. In this time period the sausage gives off water which escapes as water vapor through the casing.
During what is termed the fermentation phase, in the previous processes the atmospheric humidity is set to about 90 to 95%. In addition, the temperature in the ripening chamber is first slightly increased so that the starter cultures develop more rapidly. Starter cultures used are, in particular, acidifying homofermentative lactic acid bacteria (Lactobacillus or Pediococcus species) or nitrate-reducing Staphylococcus or Micrococcus species. Thereafter the relative humidity in the ripening chamber is reduced to about 80 to 90%. The post-ripening (in the case of standard-ripened raw sausage, typically from the 10th day after production) then proceeds at about 75% relative humidity. During ripening the sausage loses about 22 to 35% of its weight by the removal of water.
The water vapor permeability of conventional casings is so high that under not quite optimal ripening conditions, excessive drying out of the outer regions of the sausage occurs, i.e. what is termed a dry rim is formed. The atmospheric humidity is therefore kept very high in the initial phase of drying, generally above 90%. Once a dry rim has formed, it retards the further drying out of the sausage. At a pH at the isoelectric point, the sausage emulsion readily gives off water, at the same time, when this point is reached, gel formation of the meat protein starts which counteracts the release of water. For drying, the most suitable time period is therefore the time period up to reaching the isoelectric point. Using the highly permeable casings which are customary to date, the time period up to reaching the isoelectric point can only be exploited inadequately.